Span & Load Calculation
Two Loads You Must Check
Uniformly Distributed Load (UDL)
Weight spread over the panel — a crowd of pedestrians, a layer of material, an equipment mat. Specified in kN/m² (psf). Typical pedestrian walkway live load is 50–65 psf (2.4–3.1 kN/m²); crowded assembly areas are higher per your building code.
Concentrated Load (Point Load)
A single heavy point — a forklift wheel, a machine foot, a dropped load, a drum pallet. Specified in kN (lbf). It must be checked separately: a panel fine for UDL can deflect badly under one concentrated wheel.
The Deflection Criterion Is the Real Limit
FRP is more flexible than steel, so deflection — not strength — usually controls the design. The same panel carries less load when you demand a stricter deflection ratio.
| Limit | Meaning | Typical Use |
|---|---|---|
| L/100 | Deflection = 1/100 of clear span | General industrial walkways, less sensitive |
| L/150 | Deflection = 1/150 of clear span | Standard pedestrian platforms, balconies |
| L/200 | Deflection = 1/200 of clear span | Sensitive areas, machinery decks, high-crowd areas |
| 3/8 in (≈9.5 mm) absolute cap | Maximum absolute deflection regardless of span | OSHA/conservative practice for long spans |
Always confirm which deflection criterion your project specifies before comparing two load charts — they are not interchangeable.
Section Properties & Safety Factor
Section Modulus (Z) & Moment of Inertia (I)
Pultruded bearing bars act as beams: allowable load scales with Z (strength) and I (stiffness/deflection). ZeAllgrate supplies I and Z per bearing-bar series (I-4010, I-6010, I-4015, I-6015, T-3320, T-5020).
Modulus of Elasticity (E)
FRP flexural modulus depends on resin and glass content. Pultruded (~70% glass) is roughly twice as stiff as molded (~33% glass), which is why pultruded spans so much further.
Safety Factor
Apply a working-load safety factor of approximately 4:1 to 5:1 over ultimate load, per ZeAllgrate practice. Live load and impact are then checked against the reduced working load.
Calculation Checklist
| Parameter | Guidance |
|---|---|
| Support width | Minimum 40 mm bearing on the support structure at each end |
| Clip spacing | Hold-down clips at support intersections, spacing ≤ 1219 mm (48 in); minimum 4 clips per panel |
| Orientation | Pultruded bearing bars MUST run across the clear span — never parallel to it |
| Support tolerance | Framing level within ±5 mm; uneven supports add eccentric load |
| Temperature | Resin modulus drops with temperature; derate hot-service panels accordingly |
Source: ZeAllgrate (Fiberglass Grating Manufacturers Council / ACMA) design guidelines; ASTM International; ISO 14122; OSHA 29 CFR 1910. Indicative data for specification guidance only — final design verified by ZeAllgrate engineering against certified load/span charts.
Worked Span Calculation
Take a 38 mm molded panel at 600 mm clear span, L/200 limit, uniform design load 5 kN/m². Read the uniform table at 600 mm / L/200: the tabulated capacity exceeds the load, so the section passes the uniform case. Then check the concentrated case — say a 1.5 kN maintenance point load — at the same span and limit; where the point load governs, the section is confirmed against the concentrated column. The section is sized by the governing case, and the safety factor applied by the supplier is confirmed on the table header (working vs. ultimate values) before the number is used in the calculation.
Section Properties and Units
Section modulus (Z) and moment of inertia (I) come from the bar geometry and are published per panel or per bar for the design span. The elastic modulus (E) is the laminate value — roughly 1/20th of steel's — which is why deflection, not strength, drives most FRP selections. Keep units consistent: kN/m² and metres in the calculation, or psf and feet — mixing unit systems is the fastest route to a wrong section. Confirm whether table values include the supplier safety factor before applying your own.
Section modulus (Z) and moment of inertia (I) come from the bar geometry and are published per panel or per bar for the design span. The elastic modulus (E) is the laminate value — roughly 1/20th of steel's — which is why deflection, not strength, drives most FRP selections. Keep units consistent: kN/m² and metres in the calculation, or psf and feet — mixing unit systems is the fastest route to a wrong section. Confirm whether table values include the supplier safety factor before applying your own.Need Certified Load/Span Charts?
Send clear span, UDL, any point load and your deflection limit — we return the exact panel and chart.